homescreen showWindow event not reaching listeners

When I trigger the "homescreen/showWindow" operation from a web app, it never seems to reach the services listening to it.

For example, WAM is listening for this event. The handler is declared here: https://github.com/webosose/wam/blob/159cef4225664376c17a21459a1b1a01a7924a76/src/agl/WebRuntimeAGL.cpp#L320

When the Qt launcher opens a running webapp, I can see this message in the system logs:

Jul 16 10:35:51 intel-corei7-64 afbd-webapps-html5-launcher@1.0[956]: ## (DEBUG)[WebAppLauncherRuntime::init_hs()::<lambda(json_object*)>] Activesurface WebApp-31029

We are implementing an HTML5 launcher in SPEC-2401. This is the code that calls the homescreen API: https://github.com/jaragunde/agl-html5-launcher/commit/146044a5d19ef0b6f0c5cbcfce7470bf5292167b

The message returns with success status. The AFM monitor reports the message was sent and the success reply, too. But WAM never receives the event, the aforementioned log message is never printed and the window is not shown.